Organic acid treating fluids with viscoelastic surfactants and internal breakers

Abstract

An aqueous fluid system that contains an aqueous dicarboxylic acid solution, a viscoelastic surfactant as a gelling agent to increase the viscosity of the fluid, and an internal breaker such as mineral oil and/or fish oil to controllably break the viscosity of the fluid provides a self-diverting acid treatment of subterranean formations. The internal breaker may be at least one mineral oil, a polyalphaolefin oil, a saturated fatty acid, and/or is an unsaturated fatty acid. The VES gelling agent does not yield viscosity until the organic acid starts to spend. Full viscosity yield of the VES gelling agent typically occurs at about 6.0 pH. The internal breaker allows the VES gelling agent to fully viscosify the spent organic acid at 6.0 pH and higher, but as the spent-acid VES gelled fluid reaching reservoir temperature, controllable break of the VES fluid viscosity over time can be achieved.

1. A method for treating a subterranean formation comprising:
 introducing a viscoelastic surfactant gelled fluid into a subterranean formation, where the viscoelastic surfactant gelled fluid comprises:
 water; 
 at least one viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the water, where the VES is selected from the group consisting of non-ionic, cationic, and zwitterionic surfactants, where the zwitterionic surfactants are selected from the group consisting of dihydroxyl alkyl glycinate, alkyl ampho acetate or propionate, and alkylimino mono- or di-propionates; 
 at least one internal breaker selected from the group consisting of mineral oils, plant oils, fish oils, hydrogenated polyalphaolefin oils, saturated fatty acids, unsaturated fatty acids and combinations thereof; and 
 at least one dicarboxylic acid; 
 
 treating the subterranean formation with the dicarboxylic acid; and 
 reducing the viscosity of the viscoelastic surfactant gelled fluid with the breaker. 
 
     
     
       2. The method of  claim 1  where the subterranean formation contains carbonate, where the viscoelastic surfactant gelled fluid has a pH and where the treating further comprises:
 contacting the carbonate with the viscoelastic surfactant gelled fluid; 
 reacting the at least one dicarboxylic acid with the carbonate in the formation thereby increasing the fluid pH causing at least portions of the fluid to increase the local viscosity thereof; and 
 diverting unreacted dicarboxylic acid to contact further carbonate via the increased local viscosity of the fluid. 
 
     
     
       3. The method of  claim 1  further comprising:
 heating the fluid to a temperature effective to cause the breaker to reduce the viscosity of the gelled aqueous fluid. 
 
     
     
       4. The method of  claim 3  where the effective temperature ranges from about 100 to about 400° F. (about 38 to about 204° C.). 
     
     
       5. The method of  claim 1  where the internal breaker is a mineral oil and is at least about 99 wt % paraffin. 
     
     
       6. The method of  claim 1  where the internal breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
       7. The method of  claim 1  where the internal breaker is selected from the group consisting of a mineral oil, a plant oil, a fish oil and mixtures thereof, and the effective amount of the internal breaker in the fluid ranges from about 0.1 to about 15 gptg based on the total fluid. 
     
     
       8. The method of  claim 1  where the only viscosity reducing agent added is the internal breaker. 
     
     
       9. The method of  claim 1  where the internal breaker is present in an oil-soluble internal phase of the aqueous fluid. 
     
     
       10. The method of  claim 1  where the at least one dicarboxylic acid has a formula weight of 175 or less. 
     
     
       11. The method of  claim 1  where the at least one dicarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, and mixtures thereof. 
     
     
       12. The method of  claim 1  where the viscoelastic surfactant gelled fluid further comprises hydrofluoric acid or a substance that hydrolyzes to hydrofluoric acid. 
     
     
       13. A method for treating a subterranean formation comprising:
 introducing a viscoelastic surfactant gelled fluid into a subterranean formation containing carbonate, where the viscoelastic surfactant gelled fluid has a pH and comprises:
 water; 
 at least one viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the water, where the VES is selected from the group consisting of non-ionic, cationic, and zwitterionic surfactants, where the zwitterionic surfactants are selected from the group consisting of dihydroxyl alkyl glycinate, alkyl ampho acetate or propionate, and alkylimino mono- or di-propionates; 
 at least one internal breaker selected from the group consisting of mineral oils, plant oils, fish oils, hydrogenated polyalphaolefin oils, saturated fatty acids, unsaturated fatty acids and combinations thereof; and 
 at least one dicarboxylic acid having a formula weight of 175 or less; 
 
 treating the subterranean formation with the dicarboxylic acid comprising:
 contacting the carbonate with the viscoelastic surfactant gelled fluid; 
 reacting the dicarboxylic acid with the carbonate in the formation thereby increasing the fluid pH causing portions of the fluid to increasing the local viscosity thereof; and 
 diverting unreacted dicarboxylic acid to contact further carbonate via the increased local viscosity of the fluid; and 
 
 reducing the viscosity of the viscoelastic surfactant gelled fluid with the breaker. 
 
     
     
       14. The method of  claim 13  further comprising:
 heating the fluid to a temperature between about 100 to about 400° F. (about 38 to about 204° C.) causing the breaker to reduce the viscosity of the gelled aqueous fluid. 
 
     
     
       15. The method of  claim 13  where the internal breaker is a mineral oil and is at least about 99 wt % paraffin. 
     
     
       16. The method of  claim 13  where the internal breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
       17. The method of  claim 13  where the internal breaker is selected from the group consisting of a mineral oil, a plant oil, a fish oil and mixtures thereof, and the effective amount of the internal breaker in the fluid ranges from about 0.1 to about 15 gptg based on the total fluid. 
     
     
       18. The method of  claim 13  where the only viscosity reducing agent added is the internal breaker. 
     
     
       19. The method of  claim 13  where the internal breaker is present in an oil-soluble internal phase of the aqueous fluid. 
     
     
       20. The method of  claim 13  where the dicarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, and mixtures thereof. 
     
     
       21. The method of  claim 13  where the viscoelastic surfactant gelled fluid further comprises hydrofluoric acid or a substance that hydrolyzes to hydrofluoric acid. 
     
     
       22. A viscoelastic surfactant gelled fluid comprising:
 water; 
 at least one viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the water, where the VES is selected from the group consisting of non-ionic, cationic, and zwitterionic surfactants, where the zwitterionic surfactants are selected from the group consisting of dihydroxyl alkyl glycinate, alkyl ampho acetate or propionate, and alkylimino mono- or di-propionates; 
 at least one internal breaker selected from the group consisting of mineral oils, plant oils, fish oils, hydrogenated polyalphaolefin oils, saturated fatty acids, unsaturated fatty acids and combinations thereof; and 
 at least one dicarboxylic acid. 
 
     
     
       23. The viscoelastic surfactant gelled fluid of  claim 22  where the internal breaker is a mineral oil and is at least about 99 wt % paraffin. 
     
     
       24. The viscoelastic surfactant gelled fluid of  claim 22  where the internal breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
       25. The viscoelastic surfactant gelled fluid of  claim 22  where the internal breaker is selected from the group consisting of a mineral oil, a plant oil, a fish oil and mixtures thereof, and the effective amount of the internal breaker in the fluid ranges from about 0.1 to about 15 gptg based on the total fluid. 
     
     
       26. The viscoelastic surfactant gelled fluid of  claim 22  where the only viscosity reducing agent added is the internal breaker. 
     
     
       27. The viscoelastic surfactant gelled fluid of  claim 22  where the internal breaker is present in an oil-soluble internal phase of the aqueous fluid. 
     
     
       28. The viscoelastic surfactant gelled fluid of  claim 22  where the at least one dicarboxylic acid has a formula weight of 175 or less. 
     
     
       29. The viscoelastic surfactant gelled fluid of  claim 22  where the at least one dicarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, and mixtures thereof. 
     
     
       30. The viscoelastic surfactant gelled fluid of  claim 22  further comprising hydrofluoric acid or a substance that hydrolyzes to hydrofluoric acid. 
     
     
       31. The viscoelastic surfactant gelled fluid of  claim 22  where the fluid consists essentially of water, the at least one VES, the at least one internal breaker and the at least one dicarboxylic acid. 
     
     
       32. A viscoelastic surfactant gelled fluid comprising:
 water; 
 at least one amidoamine oxide viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the water; 
 at least one internal breaker selected from the group consisting of mineral oils, plant oils, fish oils, hydrogenated polyalphaolefin oils, saturated fatty acids, unsaturated fatty acids and combinations thereof, where the internal breaker acts to reduce the viscosity of the fluid when the temperature of the fluid ranges between about 100 to about 400° F. (about 38 to about 204° C.); and 
 at least one dicarboxylic acid having a formula weight of 175 or less. 
 
     
     
       33. The viscoelastic surfactant gelled fluid of  claim 32  where the internal breaker is a mineral oil and is at least about 99 wt % paraffin. 
     
     
       34. The viscoelastic surfactant gelled fluid of  claim 32  where the internal breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
       35. The viscoelastic surfactant gelled fluid of  claim 32  where the internal breaker is selected from the group consisting of a mineral oil, a plant oil, a fish oil and mixtures thereof, and the effective amount of the internal breaker in the fluid ranges from about 0.1 to about 15 gptg based on the total fluid. 
     
     
       36. The viscoelastic surfactant gelled fluid of  claim 32  where the only viscosity reducing agent added is the internal breaker. 
     
     
       37. The viscoelastic surfactant gelled fluid of  claim 32  where the internal breaker is present in an oil-soluble internal phase of the aqueous fluid. 
     
     
       38. The viscoelastic surfactant gelled fluid of  claim 32  where the at least one dicarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, and mixtures thereof. 
     
     
       39. The viscoelastic surfactant gelled fluid of  claim 32  further comprising hydrofluoric acid or a substance that hydrolyzes to hydrofluoric acid.